Vacuum tube telegraph repeater



Oct. 4, 1932. H. M. CASE VACUUM TUBE TELEGRAPH REPEATER Filed Sept. 12.1930 INVENTOR: 2 C666 ATTORNEY Patented Oct. 4, 1932 UNITED ST'E'SOFFICE HARLOW M. CASE, OF CHICAGO, ILLINOIS, ASSICrNOR TO THE WESTERNUNION TELE GRAPH COMPANY, OF NEW YORK, N. Y., A CORPORATION OF NEW YORKVACUUM TUBE TELEGRAPH REPEATER Application filed September 12, 1930.Serial No. 481,492.

This invention relates to repeaters for telegraph circuits, and inparticular to a bridge type of duplex repeater employing thermionicvacuum tubes to control the field current of a generator whose armatureis connected to the transmitting point of the bridge on the oppositeside of the repeater.

Broadly, the object of the invention is to provide novel means forreversing the field of the repeating generator in accordance withincoming signals to be repeated.

An object of the invention is to utilize the difi'erential action ofvacuum tubes connected in the arms of a normally balanced bridge networkfor controlling the polarity of current impulses applied to the line atthe transmitting point of the repeater bridge.

Another object of the invention is to make the flow of current in thearmature of the repeating generator dependent upon a condition ofinequality in the instantaneous potentials applied to the two grids or"a pair of like thermionic vacuum tubes connected across the bridge.

The invention is disclosed, in its preferred embodiment, in connectionwith a bridge type of duplex repeater working on a ground circuit. Inthe figure:

A pair of telegraph lines 1 and are connected for duplex operation byway of a repeater comprising bridge B and bridge B Bridge 13 comprisesfour arms, of which the resistances 3 and 4 form two of the arms, andline 1 and artificial line 2 the other two arms. The resistances 3 and4: are usually, though not necessarily, equal in value. Resistances 16and 17 form a potentiometer which will be discussed hereinaften.

Similarly, bridge B comprises four arms, of which line 5 and artificialline 6 are two and the resistances 7 and 8 the other two. If the line 5and balancing line 6 have equal impedances, resistances 7 and 8 shouldalso be equal.

The generator G has its armature 9 connected from ground to thetransmitting point of the bridge B which is the junction of theresistances 3 and 4. Similarly the armature 10 of generator G isconnected to ground and to the transmitting point of bridge B that is,to the junction of the resistances 7 and 8.

Generator G is thus connected across one di-' agonal of bridge B andgenerator G is connected across one diagonal of bridge B The terminalsof the second diagonal of each bridge are connected respectively to thegrids of a pair of similar thermionic vacuum tubes. Thus the junction aof line 1 and resistance 3 is connected to the grid of a vacuum tube 11while the junction Z2 of artificial line 2 and resistance 4'' isconnected to the grid of tube 12. Similarly, the grids of tubes 13 and14% are connected to the junction a of line 5 and resistance 7, and tothe junction Z2 of artificial line 6 and resistance 8, iespectively.

The filaments of tubes 11 and 12 are connected together and to aconductor 15 which extends to the electrical midpoint of a resistancehaving equal halves 16 and 17 These resistances 16 and 17 are thusconnected across the input electrodes of the two tubes 11 and 12.Resistances 16 and 17 may be considered to comprise a potentiometerwhich insures that the filaments of the tubes shall be at a potentialwhich is midway between that of the two grids when. there is anypotential drop across the potentiometer.

Similarly, thefilaments of tubes 13 and 14: across bridge B areconnected a common conductor 18 to the junction of two equal resistances19 and 20 which are connected across the input circuits of the tubes 13and 14 respectively. Resistances 19 and 20 form a potentiometer whichbrings the filaments to a potential midway between that of the grids orthat ofthe terminals of the bridge terminals a and Z2 I The plate oranode circuits of tubes 11 and 12 of bridge B are completed through acommon conductor 21 which is a continuation of conductor 15, throughbattery 22 and separately through the two field coils 23 211M124,respectively, of generator G These field coils, like vacuum tubes 11 and12, are equal or identical, but they are connected in oppositedirections to each other.

Similarly, for bridge B the plate or anode circuit of tube 13 extendsfromthe filament through conductor 18, conductor 25, battery 26 andfield coil 27 of generator G back to the plate electrode of tube 13,while the plate circuit of tube 14 extends from its filament Althoughthe elements 3, a and 7 8 are shown as resistances they could beinductances, condensers or any possible combination of'inductance,resistance and capacity which will give the desired wave form to theinput circuits of the vacuum tubes.

The operation of the circuit will be understood trom the following:" i

When the same potential, be it positive, negative or zero with respectto the filament, is applied to the grids of the tubes 11 and 12 acrossbridge B there Will be no potential across the armature 100i generator Gsince equal currents will flow from battery 22 through the field coils23 and 24 which are connected in opposite directions and the resultantfield flux will be zero.

If an incoming signal current produces a potential drop across thepoints a 6 the grids of tubes 11 and 12 will be oil opposite polaritiesand the plate currents flowing through field coils 23 and 2% will nolonger be equal. The current in one of these coils will increase andthat in the other will decrease, so that a resultant field flux is setup and-a current induced in armature 10 of generator G The inducedcurrent in armature 10 flows to line 5 and artificialline G from 1 thetransmitting point of bridge 13 over resistances 7 and 8 respectively.

When the artificial lines are adjusted to have the same impedance as thereal lines and resistances 7 and8 are equal, the armature of generator Gwill impress the same potential between the ground and points a and 6 onbridge B Accordingly the grids of tubes 13 and 14 will receive equalpotentials and the plate circuits of these tubes will be affected in thesame manner, with'the result that the currents flowing through coils 27and 28 will continue to be equal and the resultant flux in generator Gwill remain zero.

The direction of the current induced in armature 10 of generator Gdepends on which of the field coils 23 and24 has the predominatingcurrent. Then the grid of tube 11 is made positive, for example, currentin coil 23 may increase and, in predominating over the current in coil24, cause a current of positive polarity to be induced in armature 10 ofgen erator G and applied to the line 2. WVhen the grid of tube 11becomes positive with re spect to its filament, the grid of tube 12becomes negative with respect to its filament, so that the plate currentof tube 11 increases and the plate current of tube 12 decreases. Vhenthe grid of tube 11 becomes negative, that of tube 12 becomes positiveand the platecurrent of tube 11 decreases while the plate current oftube 12 increases. The current through one of the generator fieldwindings will increase and that through the other will decrease, eachwinding setting up a field flux dependent on the current flowing and thealgebraic summation of the two fluxes so produced determines themagnitude and direction of the resultant field flux. Thus the magnitudeand direction of the resultant potential across the generator armatureis determined by the polarity of the incoming signal, and the receivedsignal will be repeated in amplified form over the opposite line fromwhich it was received.

WV hen the artificial lines of the repeater are adjusted so that theyhave the same impedance characteristics as the real telegraph lines,care must be taken not only that the two bridge arms connected to thegenerator associated with the other bridge shall have the same impedancebut also that they shall have the same phase angle, in order that thecurrent induced in one generator shall not afi'ect the circuits of thetube associated with the opposite bridge.

It will be obvious that the operation for current incoming to bridge Bis the same as that described for currents incoming to bridge B Ineither case the balanced condition of the bridge connected to the'linefrom which the signal currents are received, will be upset by theapplication of unlike signal potentials to the grids of the associatedtubes. This will result in the application of current of polarity likethat of-the incoming current,

1 to the transmitting point of the balanced bridge'on the other side ofthe repeater.

' The operation as described depends on the two vacuum tubes used invthe same. bridge having the same plate current grid potentialcharacteristics. h I

' It is worthy of note that as one of the tube grids is always positiveand the other is always negative while signals are being received, thetotal impedance of the bridge network including the. input circuits ofthe tubes is constant.

I claim: V I

1. A vacuum tube repeater comprising an incoming line, a balanced bridgeconnected thereto including a pair of vacuum tube relays having normallybalanced input circuits and opposed balanced output circuits, a dynamoelectric generator, means for applying incoming signals of difl'erentpolarities to said pair of relays and means under control of saidopposed output circuits for controlling the polarity of the currentproduced in the armature of said generator in accordance with thepolarity of the signal incoming from said line.

2. A vacuum tube telegraph repeater comprising a balanced bridge, a pairof threeelectrode vacuum tubes with their grids connected to thoseterminals of said bridge to which the telegraph line and its balancingline are connected, a generator having its field differentiallycontrolled by the plate circuits of said vacuum tube and means forconnecting the armature of said generator to the output side of saidrepeater.

8. A vacuum tube telegraph repeater comprising a balanced bridge, tWoarms of which are formed by the incoming telegraph line and itsbalancing line, a pair of three-electrode vacuum tubes with their gridsconnected to the bridge terminals of said line and balancing line, agenerator having a pair of differentially connected field coils, meansfor connecting one field coil in the plate circuit of each of said tubesand means for connecting the armature of said generator to the outputside of said repeater. V

4. A vacuum tube telegraph repeater comprising a balanced bridge, twoarms of which are formed by the incoming telegraph line and itsartificial line, a pair of three-electrode vacuum tubes with theirgridsconnected respectively to the bridge terminals of said line andartificial line, resistance between said grids having its midpointconnected to the filaments of said tubes, a pair of differentiallyconnected coils in the plate circuits of said tubes, a generatorconnected to the output side of said repeater and means for controllingthe field of said generator by the differential efi'ect of said platecircuit coils.

5. A vacuum tube telegraph repeater comprising a balanced bridge twoarms of which are formed by the incoming telegraph line and itsartificial line, a pair of matched threeelectrode vacuum tubes Withtheir grids connected respectively to the bridge terminals of said lineand artificial line, a pair of like impedances connected between saidgrids and with their junction point connected to the filaments of saidtubes, the impedances being so designed as to form shaped networks inthe input circuits of said tubes, a pair of differentially connectedcoils in the plate circuits of said tubes, a generator connected to theoutput side of said repeater with its field constituted by saiddifierentially connected plate coils.

6. A vacuum tube telegraph repeater comprising a balanced bridge twoarms of which are formed by the incoming telegraph line and anartificial line, a pair of matched threeelectrode vacuum tubes withgrids connected respectively to the bridge terminals of said line andbalancing line and means for maintaining said grids at like potentialsin the absence of signal currents, a generator connected to the outputside of said repeater and means for controlling the field of saidgenerator, upon the receipt of signal poten tials, by the differentialeffect of the currents in the plate circuits of said tubes.

7. A duplex vacuum tube telegraph repeater comprising a pair of balancedbridges, each bridge comprising a line, a balancing line and a pair ofimpedance arms, a generator for each bridge connected to the junction ofsaid impedance arms, a pair of three electrode vacuum tube relays foreach bridge having their input circuits connected in normally balancedrelation to the bridge terminals of said line and balancing line, andtheir output circuits connected in opposed relation, and means forcontrolling the field of the generator connected to the opposite bridge,in accordance withthe difi'erential efiect of said opposed outputcircuits when incoming signals are received.

8. A duplex vacuum tube telegraph repeater comprising a pair of balancedbridges each bridge comprising a line, an artificial line and a pair ofimpedance arms, a generator for each bridge connected to the junction ofsaid impedance arms and comprising a pair of opposed field coils, a pairof three electrode vacuum tubes for each bridge having their gridsconnected to the bridge terminals of said line and balancing line, andtheir plates connected to said opposed field coils.

9. A duplex vacuum tube telegraph repeater comprising a pair of balancedbridges, each bridge comprising a line, a balancing line and a pair ofimpedance arms, a generator for each bridge connected to the junction ofsaid impedance arms and comprising a pair of opposed field coils, a pairof three electrode vacuum tubes for each bridge having their gridsconnected to the bridge termi- 100 nals of said line and balancing line,resistances connected between said grids and their correspondingfilaments, and means connecting the field coils of the generator in theplate circuits of said tubes.

10. A duplex vacuum tube telegraph repeater comprising a pair ofbalanced bridges, each bridge comprising a line, an artificial line, anda pair of impedance arms, a dynamo electric generator under the controlof each bridge having its armature connected to the junction of theimpedance arms of the other bridge, a pair of vacuum tubes for eachbridge having their input circuits connected to opposite points on thebridge and their output circuits each connected in series with one oftWo opposed field coils of saidgenerator, and balanced wave shapingimpedances connected in the input circuits of said pair of vacuum tubes.

11. A vacuum tube repeater comprising a balanced bridge including a pairof vacuum tube relays having balanced input circuits and opposedbalanced output circuits, a dynamo electric generator, and means undercontrol of said opposed output circuits for controlling the direction ofcurrent produced in the armature of said generator.

In testimony whereof I afiix my signature.

HARLOW M. CASE.

